The number of farms and farmers has decreased significantly
in most developed countries including the US (farming.htm).The ability of a country to potentially
export food should be indicated by the ratio of food produced to
population.I have summarized UN
production data for 2002 for wheat, rice, maize/corn, and soybeans and then
divided by the populations in foods2002.htm.The last column indicates that Argentina has
the highest ratio and would be the most likely to export.China is just above the world average
ratio.Actual historical export data for
wheat, rice, and maize/corn (exports.htm) show that
Argentina is a major exporter of wheat and maize/corn.China exports less than 10% of its production
even though it is the largest producer.In fact, many of the largest producers export very little because they
also have very large populations. In the
export tables, I have divided percent exports by percent population growth to
estimate how many years each country is likely to be able to export each food
assuming zero net immigration.Only
Argentina, Australia, Canada, and the USA have much long-term potential to
export these foods.When the percentage
world exports are divided by the world population growth rate of 1.27%/year
between 2000 and 2001, one obtains estimates that international trade will consume
the wheat exports in 13 years, the rice exports in 3 years, and the corn
exports in 10 years.

Adults use 1700 to 3000 nutritional calories (chemical
kilocalories) per day or about 2350 calories per day on average.Adolescent boys, very active men under
thirty-five, and lactating women consume about 3000 calories per day while
children one to six years require 1100 to 1600 calories per day.In the following, I assume two-thirds of the
total calories for humans come from wheat, rice, corn/maize, and soybeans or
from animals fed them.World production
of these primary foods was 1,931,665,546 metric tons in 2002.A metric ton is 1000 kilograms or 1 million
grams.Each gram of these primary foods
produces about 3 calories/gram.Thus,
the world supply of these foods could feed about

3(1.93 x 10^9)(1.00 x 10^6)/(2350)(365)

= (5.79 x
10^15)/(0.86 x 10^6) = 6.7 x 10^9 = 6.7 billion humans

if these foods were the only source of calories.However, if these foods provide only
two-thirds of the total calories, then the maximum human population might be
about 10 billion if no other animals were fed these foods. The current human
population is 6.2 billion and is increasing at about 1.27 percent per
year.Such calculations indicate that
the UN estimate of 9.3 billion humans in 2050 is at or near the limit of our
food supply.Of course, food is never
uniformly distributed, so the starvation we are seeing today will become very
wide spread before 2050 unless all countries rapidly approach zero population
growth (an average of two children per female or less).